Aluminum alloys can be grouped into two categories: heat-treatable alloys and non-heat-treatable alloys. Heat-treatable alloys are capable of being strengthened and/or hardened during an appropriate thermal treatment whereas no significant strengthening can be achieved by heating and cooling non-heat-treatable alloys. Alloys in the 2xxx, 6xxx, and 7xxx series (and some 8xxx alloys) are heat-treatable. Alloys in the 1xxx, 3xxx, 4xxx, and 5xxx series (and some 8xxx alloys) are non-heat-treatable. Hot working is plastic deformation of metal at such temperature and rate that strain hardening (i.e., cold working) does not occur.
A heat-treatable aluminum alloy component (“component”) may undergo solution heat treating. Solution heat treating may include three stages: (1) solution heating, which may include both heating and soaking (at a given temperature) of the component; (2) quenching; and (3) aging. The heating and soaking step dissolves large particles and disperses the particles as smaller precipitates or dissolved atoms (acting as soluble hardening elements) to strengthen the component. Quenching, or rapid cooling, effectively freezes or locks the dissolved elements in place (i.e., still dispersed) to produce a solid solution with more alloying elements in solution at room temperature than would otherwise occur with a slow cool down.
The aging step allows the alloying elements dissolved in the solid solution to migrate through cool metal (even at room temperature) but not as fast or as far as they could at high temperatures. Accordingly, atoms of dissolved alloying elements may slowly gather to form small precipitates with relatively short distances between them, but not large, widely-spaced particles. The quantity and high density of small dislocation-pinning precipitates gives the alloy its strength and hardness because the precipitates have a different elastic modulus compared to that of the primary element (aluminum) and thus inhibit movement of the dislocations, which are often the most significant carriers of plasticity. The aging may be natural or artificial. Some alloys reach virtually maximum strength by “natural aging” in a short time (i.e., a few days or weeks). However, at room temperature, some alloys will strengthen appreciably for years. To accelerate precipitation, these alloys undergo “artificial aging,” which includes maintaining the component for a limited time at a moderately raised temperature, which increases the mobility of dissolved elements and allows them to precipitate more rapidly than at room temperature.
Conventionally, because some alloys have poor formability (i.e., the ability to undergo plastic deformation without being damaged) at room temperature, to shape components of these alloys into desired geometric shapes, these components may undergo hot working (or hot forming) after solution heating and before quenching at temperatures at or near the solutionizing temperature. For example, see U.S. Patent Application Publication 2012/0152416 (the '416 Publication), which describes that the transfer between the heating station to the forming press should be as fast as possible to avoid heat loss from the aluminum (see paragraph and FIG. 1). Hot working or hot forming processes may include, for example, drawing, extrusion, forging, hot metal gas forming, and/or rolling.
There is a known problem with hot working some aluminum alloys (in particular, 7xxx alloys) where components exhibit unsatisfactory deformability. For example, see N. M. Doroshenko et al., Effect Of Admixtures Of Iron And Silicon on the Structure and Cracking of Near-Edge Volumes in Rolling of Large Flat Ingots from Alloy 7075, Metal Science and Heat Treatment, Vol. 47, Nos. 1-2, 2005 at 30 (“Doroshenko”). Doroshenko focuses on hot rolling of 7xxx and the resultant cracks. To address this problem, Doroshenko describes analysis and proposed guidelines for the particular chemical composition of 7xxx alloys.
There is a need for improving the deformability of aluminum alloys (particularly 7xxx alloys) during hot forming processes without exhaustive analysis and modification of the chemical composition of the alloy.